The invention relates to a fuel blocking valve device for closing a path between a fuel tank and a canister to prevent fuel from leaking when a vehicle turns over.
FIG. 4 is a schematic view showing a fuel system between a fuel tank 1 of a vehicle and a canister 2. In the drawing, on the upper portion of the tank 1, there are provided a vent valve device 5 and a blocking valve device (cut-off valve) 10 connected to the canister 2 directly by a piping 3 or through a differential pressure regulating valve 8; a pump module 4 for supplying fuel in the tank through a carburetor fuel pipe 4a; and a connecting portion and an electric system connector (not shown) of a return pipe for returning the fuel from the carburetor. Reference numeral 6 represents a fuel supply pipe, and an upper portion of the fuel supply pipe 6 and the differential pressure regulating valve 8 are connected by a piping.
The vent valve 5 is opened to discharge the fuel vapor in the tank to the canister 2 through the differential pressure regulating valve 8 when only a small amount of the fuel remains in the tank 1. When the fuel is supplied to the tank 1, the valve is closed to block the discharge of the fuel vapor. The blocking valve device 10 recovers the fuel vapor generated in the tank 1 at the canister, or prevents the fuel in the tank 1 from flowing out through the canister 2 when the vehicle turns over.
FIG. 5 is a sectional view showing the conventional blocking valve device disclosed in Japanese Patent Publication (KOKAI) No. 10-47184. The valve device 50 includes a housing 51 mounted on an upper side of the fuel tank 1 through a supporting member 52; a float valve 54 for floating to close a path communicating between an inside of the fuel tank and an outside thereof when the fuel flows into the housing; and a two-way valve 64 for opening and closing the path according to an increase or decrease in an inner pressure of the tank 1.
The housing 51 is provided with a lower chamber 53b and an upper chamber 53a divided by a valve seat 55. A float valve 54 has a valve member 56 disposed in the lower chamber 53b in a state (open state) that a spring 57 urges the valve member upward. The valve member floats when the fuel flows into the lower chamber 53b, and enters an inclined hole of a valve seat center hole 55a to become a closed position.
The two-way valve 64 includes an umbrella shape valve member 58 (having an umbrella valve 60 for a negative pressure disposed to be movable vertically) for abutting against a recessed seat portion 55b located at an upper surface of the valve seat 55 to open or close a center hole 55a; and a spring 59 for urging the valve member 58 toward a closed position.
In an operation of the valve described above, the valve member 58 is normally located at the closed position. When the inner pressure of the tank exceeds a predetermined value, the inner pressure pushes the valve member 58 to the open position against the spring 59, thereby releasing the high-pressure vapor in the fuel tank to the canister 2. When the interior of the tank becomes cool and a negative pressure, the umbrella valve 60 slides downward with respect to the valve member 58 to open the valve, thereby introducing air into the tank to release the negative pressure state.
Thus, in the valve device 50, the float valve 54 prevents the fuel from leaking when the vehicle turns over, and the two-way valve 64 controls the inner pressure of the tank.
In a case that the tank is made of a resin, a small amount of fuel vapor in the tank 1 permeates through welded portions such as attaching portions of the valve device 50 and a pump module to leak into the atmosphere. In a case that the tank is made of metal, the fuel vapor in the tank 1 permeates into the atmosphere through an introduction grommet portion of a return pipe and the like. Although the quantity of the leaked fuel vapor is extremely small, a more stringent limit value has been required in a regulation.
However, the two-way valve 64 in the conventional valve device 50 opens or closes only when the inner pressure of the tank exceeds or becomes below a predetermined value. Therefore, it is difficult to maintain the inner pressure of the tank close to the atmospheric pressure. Accordingly, the fuel vapor leaks corresponding to the situation that the inner pressure of the tank 1 becomes higher than the atmospheric pressure.
In view of the above problems, the present invention has been made, and an object of the invention is to provide a fuel blocking valve device for maintaining the inner pressure of the tank at a value close to the atmospheric pressure, thereby preventing a large amount of the fuel vapor from leaking.
Further objects and advantages of the invention will be apparent from the following description of the invention.